GLSL Sound 04 - 和音を作るテスト

sound04.glsl

#define TAU (2.*3.14159265)
float DB(float db) { return pow(10.0, db/10.0); }

float sawWave(float phase)
{
  return fract(TAU*phase);
}

float chordWave(float phase, int chord, int key)
{
  float wave;
  for (int i = 1; i <= 32; i++)
  {
    if ((chord % 2) != 0)
    {
      wave += sawWave(phase * exp2(float(i+key)/12.0));
    }
    chord /= 2;
  }
  return wave;
}

vec2 mainSound(float time){
  #define bpm 60.0
  #define STEP 2.0
  #define BAR_STEP 16.0
    
  int keyCount = 4;
  int[] keys = int[](
    0,-2,0,2
    );
  float amp = fract(time * bpm/60.0);
  amp = pow(amp, 4.0);
  
  int noteCount = 4;
  int[] notes = int[](
     (1 << 1+12) + (1 << 6+12) + (1 << 10+12),
     (1 << 6   ) + (1 << 6+12) + (1 << 10+12) + (1 << 10 + 12),
     (1 << 1+12) + (1 << 6+12) + (1 << 10+12),
     (1 << 6   ) + (1 << 6+12) + (1 << 10+12)
    );
  
  int noteIndex = (int(time*bpm/60.0/STEP)) % noteCount;
  int chord = notes[noteIndex];
  int key = -2 - 48 + keys[(int(time*bpm/60.0/BAR_STEP)) % keyCount];
  
  float wave = chordWave(440.0/2.0 * time, chord, key) * amp;
  return vec2(wave * DB(-3.0));
}